The present invention relates to analog recorders and more specifically to the recording of digital information on analog recorders.
Many analog recorders employ multiplexing schemes to record a plurality of signals onto their various channels. More multiplexing schemes employ a technique where each input signal is given its own sub-channel on each input to the analog recorder. A unique base line is assigned to each input by the addition of a unique voltage. Since each signal is given its own base line, adjustments are included to position the signals across the recording surface. Gain adjustments are also included in order to adjust the maximum relative amplitude of each sub-channel.
All of the aforementioned adjustments are not necessary when recording digital information. Gain positions are not needed since the digital inputs are always the same in amplitude. Assigning a unique base line to each channel is also unnecessary since all digital inputs have the same zero reference level. Having these adjustments only adds to th size, complexity, and cost of the multiplexer. There are also drift problems encountered when using gain and position adjustments. Because of the complexity of this type of multiplexer, initial adjustments require a great deal of time. Circuit complexity also adds to the unreliability of the multiplexer.